Constant false alarm rate (CFAR) radar detectors are well known in the art for maintaining a consistent probability of false target detection in various environments. The basic approach is to set an alarm threshold for a range cell under test by averaging the signal levels in adjacent range cells within a predetermined window centered on the cell under test.
Abrupt transitions between one level of clutter and another, for instance a transition from a grassy field to a grove of trees, are a particular problem for CFAR detectors. Pure range averaging detectors tend to alter the alarm threshold too slowly in response to abrupt clutter transitions and so to produce false detections. A "greatest-of" averaging technique obtains range averages from two windows, one on either side of the cell under test, and uses the greater of the two averages to set the threshold. This technique avoids false detections at abrupt transitions, but desensitizes the detector by excessively adjusting the threshold near such transitions. In addition, various adaptive CFAR detectors are available, but they are not directed at, nor do they solve the problem of clutter transitions.